5KTQ Overheating - need help

[A.M. "TEX" Terry, II]

Steve asked:
> Clogged rad?  Wrong/failed t-stat?  Busted water pump?  Blown head gasket
> (yikes)?

Connect a radiator testor to the fill cap, pump up to the pressure rating
of the cap, and watch to see if the pressure leaks down (shows  leak
possible in hose connection, radiator, heater, or head gasket for example).
 Use the testor to also check the radiator cap capability of holding the
designated pressure.  A bad cap could be letting coolant escape after
reaching a lower pressure range than Do all the above with the engine off.
Then connect back the testor to the radiator, again pump up to the rated
pressure.  Start the engine, let run at idle, and watch the testor gauge
needle.  If the needle fluctuates, then the engine compression is forcing
pressure into the radiator (possible blown head gasket or block).  Now
bring the rpms up to about 1500 and hold there.  Look at the testor needle
for fluctuation.  Watch the temp gauge also and see if you have any
correlation between the needle fluctuation and the temp range.  You may
have a small leak that only shows up after a certain temp range is reached.
 A faulty thermostat (not opening soon enough) may be allowing the engine
to get too hot before trying to circulate coolant, then the fan is not
cooling fast enough to keep hot fluid from being expelled since the steam
pressure is alowing escape out the cap.

Tex Terry, II
83 5kt sedan (non-quattro)
Franklin, PA  USA